The present invention relates generally to micro-electro-mechanical devices, and more particularly, to a system and method for securing and controlling an electrostatically driven micro-mirror.
In fiber-optic switches, a micro-mirror is used which has a very reflective top surface that reflects an incoming electromagnetic radiation to a desired direction. The micro-mirror is usually supported by a set of springs to maintain the position of the micro-mirror. For example, FIG. 1 illustrates an example of a conventional method for securing a micro-mirror 10. The micro-mirror 10 is secured by two linear springs 12, and can rotate along an axis formed along the two springs. Other variations of the micro-mirror are also known in the industry.
Unfortunately, these prior art methods for securing and controlling the micro-mirror tend to be unstable under electrostatic actuation due to a so-called “Avalanche” effect wherein the electro-static force dominantly takes over other restoring forces. Moreover, another drawback for most of these methods and systems is that they allow the micro-mirror to rotate along only one pre-determined axis, thereby greatly limiting the directions that one micro-mirror can reflect the electromagnetic radiation into. This limitation leads to the necessary inclusion of multiple micro-mirrors in a fiber-optic switch in order to reflect the radiation in multiple directions, thus adding significant cost to the fiber-optic switch manufacturers.
Another limitation of the conventional method is that the micro-mirror tends to have a so-called “stiction” problem wherein the micro-mirror is “stuck” to a surrounding surface undesirably and is unable to restore back to its previous position(s). In FIG. 1, the dotted line 14 shows the position of the micro-mirror in a “stuck” position wherein the micro-mirror is basically “bonded” to the surface 15 underneath (or above) the micro-mirror. As such, the micro-mirror becomes irreversibly dysfunctional, and the entire package of one or more micro-mirrors in the switch will have to be replaced.
What is needed is an efficient method and system for securing and more flexibly controlling a micro-mirror in the fiber-optic switch to reflect the electromagnetic radiation with more than one rotational degree of freedom.